Re: [RFC] madvise(MADV_TRUNCATE)

[Badari Pulavarty <pbadari@us.ibm.com>]

Andrew Morton wrote:
> Andrea Arcangeli <andrea@suse.de> wrote:
> 
>>>- View it as a filesystem operation which has MM side-effects.
>>
>> I suggested the fs operation too but then it's more efficient to have it
>> as a mm operation with fs side effects, because they don't immediatly
>> know fd and physical offset of the range. It's possible to fixup in
>> userland and to use the fs operation but it's more expensive, the vmas
>> are already in the kernel and we can use them.
> 
> 
> hm, so we have a somewhat awkward interface to a very specific thing to
> benefit a closed-source app.  That'll go down well ;)
> 

I am not sure how apps can work out (fd, phys off, len) for a given
shared memory segment range easily.

> ho-hum.  Can we think of a better name than MADV_TRUNCATE please?  Dunno
> what - MADV_REMOVE?

how about - MADV_DISCARD :) Just kidding - MADV_REMOVE is a good
name.

I am still not clear on the consensus here - the plan is go forward
with the patch (ofcourse, naming changes) and may be later add
(fd, offset, len) version of it through sys_holepunch ?

If so, I can quickly redo my patch + I need to work out bugs in
shm_truncate_range().

Thanks,
Badari

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